The present invention relates to an apparatus, process, and system for encapsulating electronic parts, and more specifically to an apparatus and process that uses changes in air pressure to force material under and around an electronic integrated circuit chip and that maintains a clean condition to both the chip and substrate during and after the process.
The need for denser, larger and more durable chip assemblies has broadened the use of Direct Chip Attach (DCA) technology to include flip chip integrated circuits. A typical flip chip integrated circuit utilizes a solder ball grid array to provide electrical connections between a die of the flip chip and a substrate. During manufacturing of a typical flip chip, after the flip chip is assembled on a substrate, a liquid dispensing system is used to apply an underfill encapsulant material between the die and the substrate. The flip chip underfill material is used to reduce mechanical and thermal stress on the electrical connections and to protect the electrical connections against atmospheric conditions. The underfill material provides stability and rigidity to the assembled flip chip and may also be used as a heat conductor to improve thermal performance of the flip chip.
In typical prior art flip chip underfilling processes, a dispenser system is used to dispense underfill material around the sides of the flip chip and the underfill material spreads under the flip chip and around the solder balls of the grid array via capillary action or xe2x80x9cwickingxe2x80x9d. During the assembly process, the substrate is typically heated prior to, during, and after dispensing of the underfill material to a temperature ranging from ambient conditions to approximately 120xc2x0 C. The heating of the substrate increases the capillary action causing the underfill material to flow further under the die of the flip chip. A final fillet of underfill material is applied around the sides of the flip chip after the wicking action has occurred. A drawback associated with such underfilling processes is that the underfill material may not completely fill all voids between a die and a substrate in a flip chip. For example, the underfill material can fail to fill spaces between the contacts of a die.
To overcome the problem of voids or air gaps, one prior art dispensing system developed by Tessera of San Jose, Calif. utilizes a vacuum approach to completely underfill flip chips. In this prior art system, the dispensing system, including one or more flip chips that are to receive underfill material, is enclosed within an air tight chamber, and prior to the dispensing of underfill material, a vacuum pump is used to purge all air from the chamber to create a vacuum. The underfill material is then dispensed around all sides of the flip chips, and the chamber is returned to ambient pressure. When the chamber is returned to ambient air pressure, the underfill material is forced under the flip chips by the difference in air pressure outside the flip chips and under the flip chips.
While the above described prior art system is effective in preventing voids in underfill material in flip chips, the system is relatively large and the time required to purge air from the air tight chamber is rather long. Further, because the airtight chamber is so large, it is difficult to effectively purge air from the chamber. In addition, the air tight chamber of the prior art accommodates only manual loading of the flip chips into the chamber, preventing the dispensing system contained within the chamber from being effectively used in an automated assembly line. Moreover, the large size of the airtight chamber often precludes it from easy integration into automated manufacturing processes.
An additional system for encapsulating electronic components such as flip chips is described in U.S. Pat. No. 6,000,924, the contents of which are incorporated herein by reference. The system described in the patent uses a special mold to seal the chip against the substrate during encapsulation. The system includes a resilient bumper means to maintain the seal of the mold around the chip, and, encapsulant is injected by the system an elevated pressure. However, this patent does not address the problem of keeping the chip and substrate in a clean condition.
Another drawback associated with such underfilling processes is that the underfill material often contaminates the chip and the substrate during and after the underfill process. The time required to restore the chip and substrate to a clean condition lengthens the manufacturing process and increases the manufacturing cost. In addition, any contaminants that remain on the chip or substrate may degrade the performance of the chip.
In one aspect, the present invention overcomes disadvantages of the prior art by providing a system, apparatus and process for encapsulating flip chips using dispensing systems having fixtures operating cooperatively with injection and vacuum valves to overcome drawbacks of the prior art systems.
In one embodiment of this aspect, a dispensing system includes a controller, a vacuum source in electrical communication with the controller, the vacuum source applying a vacuum to at least a portion of the substrate in response to an instruction from the controller, and an injector in electrical communication with the controller and having a vacuum port in communication with the vacuum source, the injector comprising a valve in communication with a pressure source and a material source, the valve permitting material to be dispensed from the material source onto a substrate in accordance with an instruction from the controller.
In another aspect, the present invention provides systems, methods, and devices for individually underfilling and/or encapsulating flip-chips in a vacuum environment while maintaining a clean condition to both the chip and the substrate during the underfill process and after the underfill process is complete. A system implemented in accordance with one embodiment of the present invention comprises a tooling mechanism, gasket, pressure pad, and an injector capable of puncturing a film held against a surface of the tooling mechanism. The gasket and tooling mechanism work in connection with a film disposed between the underfill system and the gasket to improve the cleanliness of the flip chip and substrate. Dispensing needles project through the film to dispense encapsulant to the chip disposed below the film, while the film helps prevent excess encapsulant from flowing onto the chip itself.
In another embodiment of this aspect, the invention provides a method for underfilling or encapsulating a component, such as a chip mounted on a substrate. A film sized to cover at least a portion of the component is disposed at a first location. An injector, which includes an injection needle and a vacuum needle, each of which is capable of puncturing the film is projected through the film to pierce the film, and after piercing the injector remains at least partially projecting through the film. A pressure pad at the first location helps hold the film in a substantially fixed position so that the injector can pierce the film. The injector, together with the film through which it is projected, is moved to a second location, and a component to be underfilled is placed in a fixture at the first location. Then, the injector with film is moved from the second location towards the first location. The pressure pad seals the film against a surface of the component, so that the injector is disposed in a location to underfill the component. The injector then injects underfill material around the surface of the component to be underfilled. During and after the underfill process, the film helps prevent underfill material from contacting surfaces other than the surfaces to be underfilled.
In another aspect, the present invention provides an apparatus for adding encapsulant material to a component attached to a substrate. The apparatus comprises an injector, a fixture, and a sheet of substantially taut film. The injector has an injecting outlet with an injecting tip through which encapsulant material is injected to a process area on the substrate and an air inlet with an inlet tip through which air is drawn from a process area on the substrate. The fixture is in communication with the injecting outlet and the air inlet and includes a receptacle for receiving the substrate and a gasket capable of forming a seal around at least a portion of the injecting outlet and vacuum outlet. The film is disposed between the injector and a substrate placed in the receptacle of the fixture, such that, when the injector is in a position for dispensing encapsulant to the process area on the substrate, at least the injecting tip and the inlet tip of the injector project through the substantially taut film to the process area.
In an embodiment of this aspect, the apparatus further comprises a pressure pad structured and arranged to pull the sheet of film substantially taut when the film is disposed adjacent the pressure pad. In another embodiment, the injecting tip and inlet tip are constructed and arranged to retract through the substantially taut film when dispensing of the encapsulant is complete. In still another embodiment, the apparatus includes a film moving member, such as a roller system, for disposing the film between the injector and the receptacle.
In another aspect, the present invention provides an apparatus for adding encapsulant material to a component attached to a substrate, where the substrate has a sheet of film covering a process area on the substrate. This apparatus comprises and injector and a fixture. The injector has an injecting outlet with an injecting tip through which encapsulant material is injected to a process area on the substrate and an air inlet with an inlet tip through which air is drawn from a process area on the substrate. The fixture is in communication with the injecting outlet and the air inlet and includes a receptacle for receiving the substrate and a gasket capable of forming a seal around at least a portion of the injecting outlet and vacuum outlet. The fixture is structured and arranged so that when the injector is in a position for dispensing encapsulant to the process area on the substrate, at least the injecting tip and the inlet tip of the injector project through the film on the substrate to the process area.
In still another aspect, the present invention provides a method for adding encapsulant material to a component attached to a substrate. An injector having an injecting outlet and an air inlet is provided, where the injecting outlet is capable of injecting encapsulant material to a process area on the substrate and the air inlet is outlet capable of drawing air from a process area on the substrate. A fixture for receiving the substrate also is provided, where the fixture includes a receptacle for receiving the substrate and a gasket capable of forming a seal around at least a portion of the injecting outlet and air inlet. A sheet of substantially taut film is disposed in the fixture between the injector and the receptacle.
Using the gasket, a seal is formed between the injecting outlet and the air inlet. At least a portion of the injecting outlet and air inlet is projected through the film. When a substrate having an attached component and a process area is provided in the receptacle of the fixture, the injecting outlet and the air inlet are moved to a dispensing position for the process area of the substrate, whereby the injecting outlet and air inlet project through the film to the process area. Then, encapsulating material is dispensed from the injecting outlet into a process area on the substrate, and air is drawn from the process area using the air inlet, to draw the encapsulating material through the process area.
Embodiments of this aspect can include the following. In one embodiment, the injecting outlet and air inlet are retracted from the substrate when dispensing is substantially complete. In another embodiment. In another embodiment, retracting the film sealed to the injecting outlet and air inlet retracts the injecting outlet and air inlet from the substrate. In still another embodiment, the injecting outlet and air inlet are retracted back through the film. In yet another embodiment, the film is removed from the fixture. In additional embodiments, the air inlet and the injecting outlet pierce through the film to project through the film, or can project through respective holes formed in the film.
In still another aspect, the present invention includes an apparatus for adding encapsulant material to a component attached to a substrate. This apparatus includes a means for a means for injecting encapsulant material to a process area on the substrate, a means for holding the substrate while encapsulant material is added, a means for forming a seal around at least a portion of the outlet and inlet of the injecting means, and a means for forming a barrier between the holding means and the injecting means.
The injecting means, which is is in communication with the holding means, includes an outlet for dispensing encapsulant material to a process area on the substrate and an inlet for drawing air from a process area on the substrate. The barrier means prevents encapsulant material from contaminating the receiving means and areas of the substrate outside of the process area and permits the outlet and the inlet to access the process area of the substrate.
Embodiments of this aspect include the following. In one embodiment, the apparatus further comprises a means for applying pressure to the barrier means so that the barrier is substantially taut when the barrier means is disposed adjacent the pressure means. In another embodiment, the barrier means is disposed on a surface of the substrate. In still another embodiment, the inlet and outlet are constructed and arranged to pass through the barrier means for dispensing encapsulant and pass back through the barrier means when dispensing of the encapsulant is complete. In yet another embodiment, the apparatus further comprises a barrier moving means for moving the barrier means to and from a position between the injecting means and the holding means.
The foregoing and other objects, aspects, features, and advantages of the invention will become more apparent from the following description and from the claims.